The present disclosure relates generally to aerodynamic surfaces and, more particularly, to continuous surfaces for eliminating gaps between relatively movable components of a flight vehicle.
Conventional aircraft typically include a variety of movable aerodynamic devices for controlling the pitch, yaw and roll of the aircraft and for altering the lift characteristics of the aircraft. For example, fixed wing aircraft may include ailerons mounted to the trailing edge of the wings for roll control of the aircraft. The wings may also include flaps or slats mounted to the leading edge of the wings and which may be deployed or deflected downwardly from the wings during certain phases of flight in order to maintain airflow over the wing at high angles of attack.
Flaps may be also mounted to the trailing edges of the wings to increase the amount of lift generated by the wings when the aircraft is moving through the air at relatively slow speeds. Trailing edge flaps are typically deflected downwardly during takeoff to increase lift and are then retracted during the cruise portion of a flight. The flaps may again be deflected downwardly during the approach and landing phases of the flight to reduce the landing speed of the aircraft.
Although generally effective for reducing the landing speed of an aircraft, the deflection of conventional flaps may produce several undesirable effects, Such undesirable effects may be attributed to gaps that are created between the side edges of the deployed flaps and the wings. For example, the flow of air around the relatively sharp side edges of a deflected flap may result in formation of vortices along the side edges. Such vortices may increase the aerodynamic drag of the flap, which may reduce the aerodynamic efficiency of the wing. The vortices may also cause vibration and flutter in the flap, which may have an undesirable effect on the flap actuation mechanism.
Even further, vortices that may form along the side edge of a deflected flap may generate a significant amount of noise. Although flap noise may have minimal impact when the aircraft is at high altitudes or is flying over unpopulated areas, the noise generated by deployed flaps may have a greater impact when the aircraft is near populated areas located underneath the landing pattern of an airport. In this regard, flap noise may comprise a significant portion of the overall noise generated by the aircraft during the approach and landing phases of flight when the engines are typically idling.
Continuous mold lines have been considered for use between a wing and the edge of a flap. The continuous mold line provides a continuous surface between the wing and the flap edge to reduce noise caused by air passing by a gap formed between the wing and the flap edge. Such continuous mold lines included flexible rods (made, e.g., of quartz, epoxy or composites) embedded in an elastomeric skin.
However, these continuous mold lines were employed in conjunction with relatively large actuators which bend the flexible rods and overcome the biasing force of the elastomer. For example, the actuation mechanism may comprise a rigid plunger that moves the control surface in response to an actuation force produced mechanically, electromechanically or hydraulically. The drawback to this is that such actuators are sized for the specific loads and power required to move the control surface and would need to be sized much larger to apply the force necessary to move an attached continuous surface.
Another drawback is the poor performance of elastomeric skins in cold temperatures. In low temperatures (i.e., at altitude), the elastomer can lose some flexibility and not immediately return to its original, non-deformed shape.
More recently, fiberglass strands were used in place of the flexible rods. However, the use of fiberglass strands does not overcome the large actuator and cold temperature issues.
Accordingly, there is a need for improved systems and methods for employing continuous surface technology on aircraft which do not require large actuators and in which the elastomeric skins perform better in cold temperatures.